Reciprocating internal combustion (IC) engines are known for converting chemical energy stored in a fuel supply into mechanical shaft power. A fuel-oxidizer mixture is received in a variable volume of an IC engine defined by a piston translating within a cylinder bore. The fuel-oxidizer mixture burns inside the variable volume to convert chemical energy in the mixture into heat. In turn, expansion of the combustion products within the variable volume performs work on the piston, which may be transferred to an output shaft of the IC engine.
Some constituents in the exhaust stream from an IC engine, such as, for example, nitrogen oxides (NOx), unburned hydrocarbons (UHCs), and particulate matter (PM), may be subject to government regulations. Accordingly, operators may wish to control concentrations of regulated exhaust constituents discharged to the environment. The composition of exhaust discharged from an IC engine may be affected by control of the combustion process within the variable volume combustion chamber, exhaust aftertreatment downstream of the combustion chamber, or combinations thereof. Exhaust aftertreatment devices such as selective catalytic reduction (SCR) catalysts, oxidation catalysts, particulate filters, three-way catalysts, and NOx adsorbers are known for trapping and/or converting exhaust constituents to control the composition of exhaust discharged to the environment from an IC engine.
U.S. Pat. No. 7,661,263 (the '263 patent), entitled “Method of Operating an Internal Combustion Engine,” describes a method for operating an internal combustion engine in more than one combustion mode. An exhaust system of the '263 patent may include a NOx adsorber and a bypass path that enables the exhaust stream to be routed around the NOx adsorber. According to the '263 patent, the exhaust stream may avoid the NOx adsorber via the bypass path when the engine operates in a first combustion mode, and the exhaust stream may be directed into contact with the NOx adsorber when the engine operates in a mode other than the first combustion mode. Further according to the '263 patent, the NOx adsorber may be regenerated by running the engine in a rich condition.
However, apparatus and methods are desired for regenerating a NOx adsorber independent of engine operating conditions. Accordingly, the present disclosure addresses the aforementioned concern and/or other problems in the art.